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      js中的防抖与节流
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        <h5 id="防抖与节流形成过程"><a href="#防抖与节流形成过程" class="headerlink" title="防抖与节流形成过程"></a>防抖与节流形成过程</h5><p>首先在介绍防抖与节流之前，我们要清楚为什么我们需要它们？</p>
<p>在前端有许多高频事件比如 onscroll oninput resize onkeyup keydown…,这样执行频率比较高，还比如有一些输入框联想查询，我们不需要一输就发送ajax，我们要等待输入稳定时在进行输入，这是我们想要的。。</p>
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<p>scroll和resize行为也会导致页面不断的重新渲染，如果在绑定的回调函数中大量操作dom会导致出现页面卡顿。。</p>
<p>这些都需要我们进行优化，这时候防抖（throttle），节流（debounce）就出现了</p>
<h5 id="函数节流（Throttle）"><a href="#函数节流（Throttle）" class="headerlink" title="函数节流（Throttle）"></a>函数节流（Throttle）</h5><p>节流就是保证一段时间内，核心代码只执行一次<br>打个比方：水滴积攒到一定重量才会下落</p>
<h6 id="简易节流函数"><a href="#简易节流函数" class="headerlink" title="简易节流函数"></a>简易节流函数</h6><figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">button</span> <span class="attr">id</span>=<span class="string">&quot;btn&quot;</span>&gt;</span>快速点击<span class="tag">&lt;/<span class="name">button</span>&gt;</span></span><br><span class="line"></span><br></pre></td></tr></table></figure>
<p>实现一秒内点击一次</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> btn = <span class="built_in">document</span>.getElementById(<span class="string">&#x27;btn&#x27;</span>);</span><br><span class="line">   <span class="function"><span class="keyword">function</span> <span class="title">throttle</span>(<span class="params">func,wait</span>)</span>&#123;</span><br><span class="line">       <span class="keyword">let</span> previous = <span class="number">0</span>;</span><br><span class="line">       <span class="keyword">return</span> <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">           <span class="keyword">let</span> now = <span class="built_in">Date</span>.now();</span><br><span class="line">           <span class="keyword">if</span>(now - previous &gt; wait)&#123;</span><br><span class="line">               func.apply(<span class="built_in">this</span>,<span class="built_in">arguments</span>);</span><br><span class="line">               previous  = now;</span><br><span class="line">           &#125;</span><br><span class="line">       &#125;</span><br><span class="line">   &#125;</span><br><span class="line">   <span class="function"><span class="keyword">function</span> <span class="title">logger</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="built_in">console</span>(<span class="string">&#x27;logger&#x27;</span>)</span><br><span class="line">   &#125;</span><br><span class="line">   btn.addEventListener(<span class="string">&#x27;click&#x27;</span>,throttle(logger,<span class="number">1000</span>));</span><br><span class="line"></span><br></pre></td></tr></table></figure>
<h6 id="节流函数完整版"><a href="#节流函数完整版" class="headerlink" title="节流函数完整版"></a>节流函数完整版</h6><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 实现了 trailing 最后一次点出会触发事件,leading:第一次点击不生效</span></span><br><span class="line">   <span class="keyword">let</span> btn = <span class="built_in">document</span>.getElementById(<span class="string">&#x27;btn&#x27;</span>);</span><br><span class="line">    <span class="function"><span class="keyword">function</span> <span class="title">throttle</span>(<span class="params">func,wait,options</span>)</span>&#123;</span><br><span class="line">        <span class="comment">// trailing 最后一次触发</span></span><br><span class="line">        <span class="keyword">let</span> args , context,previous = <span class="number">0</span>,timeout; <span class="comment">//将参数，函数上下文进行保存</span></span><br><span class="line">        <span class="keyword">let</span> later = <span class="function"><span class="keyword">function</span> (<span class="params"></span>)</span>&#123;</span><br><span class="line">            previous = options.leading === <span class="literal">false</span> ? <span class="number">0</span>:<span class="built_in">Date</span>.now();</span><br><span class="line">            func.apply(context,args);</span><br><span class="line">            args =context = <span class="literal">null</span>;</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">let</span> throttled = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">           args = <span class="built_in">arguments</span>;</span><br><span class="line">           context = <span class="built_in">this</span>;</span><br><span class="line">           <span class="keyword">let</span> now =  <span class="built_in">Date</span>.now();</span><br><span class="line">           <span class="keyword">if</span>(!previous &amp;&amp; options.leading === <span class="literal">false</span>) previous = now;</span><br><span class="line">           <span class="keyword">let</span> remain = wait -  (now - previous);</span><br><span class="line">        </span><br><span class="line">           <span class="keyword">if</span>(remain &lt;=<span class="number">0</span>)&#123; <span class="comment">//第一次</span></span><br><span class="line">           <span class="keyword">if</span>(timeout)&#123;</span><br><span class="line">               <span class="built_in">clearTimeout</span>(timeout);</span><br><span class="line">               timeout = <span class="literal">null</span>;</span><br><span class="line">           &#125;</span><br><span class="line">            func.apply(context,args);</span><br><span class="line">            previous = now;</span><br><span class="line">           &#125;<span class="keyword">else</span> <span class="keyword">if</span>(!timeout &amp;&amp; options.trailing !== <span class="literal">false</span>)&#123; <span class="comment">//最后一次点出会触发事件</span></span><br><span class="line">            timeout = <span class="built_in">setTimeout</span>(later,remain);</span><br><span class="line">           &#125;</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">return</span> throttled;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">function</span> <span class="title">logger</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">     <span class="built_in">console</span>(<span class="string">&#x27;logger&#x27;</span>)</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="comment">//  leading:false ：第一次点击不生效</span></span><br><span class="line">    </span><br><span class="line">    btn.addEventListener(<span class="string">&#x27;click&#x27;</span>,throttle(logger,<span class="number">1000</span>,&#123; <span class="attr">leading</span>:<span class="literal">false</span> &#125;));</span><br></pre></td></tr></table></figure>

<h5 id="函数防抖（Debounce）"><a href="#函数防抖（Debounce）" class="headerlink" title="函数防抖（Debounce）"></a>函数防抖（Debounce）</h5><p>防抖就是一段时间结束后，才能触发一次，如果一段时间未结束再次触发，就会重新开始计算时间。<br>打个比方: 你在做电梯，门快要关了，突然有人准备上来。电梯门会重新打开，延迟了电梯门关闭时间，上来之后就重新关闭。</p>
<h6 id="防抖函数"><a href="#防抖函数" class="headerlink" title="防抖函数"></a>防抖函数</h6><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">debouce</span>(<span class="params">func,wait,immediate</span>)</span>&#123;</span><br><span class="line">    <span class="keyword">let</span> timeout;</span><br><span class="line">    <span class="keyword">return</span> <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">        <span class="built_in">clearTimeout</span>(timeout); <span class="comment">//重新开始计时</span></span><br><span class="line">        <span class="keyword">if</span>(immediate)&#123;</span><br><span class="line">            <span class="keyword">let</span> collNow = !time;</span><br><span class="line">            <span class="keyword">if</span>(collNow) func.apply(<span class="built_in">this</span>,<span class="built_in">arguments</span>);</span><br><span class="line">        &#125;</span><br><span class="line">        timeout  = <span class="built_in">setTimeout</span>(<span class="function">()=&gt;</span>&#123;</span><br><span class="line">            func.apply(<span class="built_in">this</span>,<span class="built_in">arguments</span>);</span><br><span class="line">        &#125;,wait)</span><br><span class="line">    &#125;</span><br><span class="line">&#125; </span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">logger</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="built_in">console</span>(<span class="string">&#x27;logger&#x27;</span>)</span><br><span class="line">   &#125;</span><br><span class="line">   <span class="comment">// 第三个参数表示首次先触发一下</span></span><br><span class="line">btn.addEventListener(<span class="string">&#x27;click&#x27;</span>,debounce(logger,<span class="number">1000</span>,<span class="literal">true</span>)</span><br><span class="line"></span><br></pre></td></tr></table></figure>

      
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